1. Field of the Invention
The present invention relates to an air bag device for an automotive vehicle. To protect an occupant of a passenger seat in a front passenger compartment during a collision of an automotive vehicle, an air bag device may be installed in a space inside an instrument panel structure, through an opening of the instrument panel structure located in a position in front of the passenger seat. Such an air bag device typically has an air bag which is inflated and unfolds toward the passenger seat of the automotive vehicle through the opening of the instrument panel structure so as to restrain and protect the occupant sitting on the passenger seat upon the occurrence of a collision.
The opening of the instrument panel structure is typically closed off by an air bag lid from the front passenger compartment, so as to cover and protect the air bag device from damage. When a collision occurs, the air bag lid is opened towards the front passenger compartment by the inflating air bag, allowing the air bag to unfold.
2. Description of Related Art
The structure of such an air bag lid may be either an integral type of structure, in which an integral lid opens upwards or downwards about either a lower or an upper end about a hinge when the air bag unfolds, or a two-part or double-leafed hinged type of structure, such as is described in, for example, Japanese Unexamined Patent Publication No. 63-258240. Such a double-leafed hinged lid includes an upper lid capable of opening upwards, and a lower lid, capable of opening downwards. Because the air bag lids project into the passenger compartment, on opening, only a small distance and, accordingly, the degree of design freedom of the instrument panel structure is high, the double-leafed hinged type of air bag lid has been widely adopted.
Two kinds of structures for such double-leafed hinged air bag lids are well known. One well known type of double-leafed hinged air bag lid has an upper lid portion and a lower lid portion which are, initially, made as a single part formed with a weakened breakable line. When the air bag unfolds, the air bag lid is broken along the weakened breakable line so as to open upward and downward in two parts and uncover the opening in the instrument panel structure. The other well known type of double-leafed hinged air bag lid has an upper lid and a lower lid which are formed completely separately.
The first kind of double-leafed hinged air bag lid has at least one potential problem. Specifically, the first kind of double-leafed hinged air bag lid, during opening, may not rupture the outer cover skin which covers the surface of the air bag lid completely, and there exists the disadvantage that fragments of the ruptured outer cover skin will fly apart into the passenger compartment of the vehicle. The second kind of air bag lid does not have such a disadvantage and, therefore, is considered to have greater practical utility
In this kind of completely separated or divided double-leafed hinged air bag lid, the upper end portion of the upper lid and the lower end portion of the lower lid are typically hinged to the instrument panel structure, and the lower end of the upper lid and the upper end of the lower lid are not usually connected to each other.
If the completely divided, double-leafed hinged air bag lid is mounted on a part of the vehicle body, with the lower end of the upper lid and the upper end of the lower lid positively disconnected, it is difficult to place these upper and lower lids accurately in their desired relative positions. For example, with the completely divided, double-leafed hinged air bag lid assembled to or installed in the vehicle body, facing end portions of the upper lid and the lower lid, and adjacent portions of each of these lids and the margins of the instrument panel around the opening, have a difference in level, or a gap difference, between their flat surfaces. In other words, the clearance left between the lids is not uniform in dimension. Such a dimensional nonuniformity in the clearance between the instrument panel and the air bag lid impairs the external appearance of the air bag device.
Furthermore, when the air bag is considered from a structural viewpoint, the rigidity of a hinge structure of the joined portion between the upper and lower lids is low, and there is a chance that the inside of the instrument panel structure, where the air bag device is installed from outside vehicle interior, and the region within the air bag cover, can be accessed through the clearance between the joined portions. For example, while the air bag device is covered, the air bag lid may be intentionally opened by, for example, inserting a foreign body, such as a steel wire or the like, through the clearance, and pulling the same. In some such cases, the air bag contained inside the instrument panel structure might be damaged.